Casing deformation risk assessment method based on fault–slip theory and its application to shale formations

This study establishes a calculation method for the critical disturbance pressure and activation angle of fractures and quantitatively simulates the influence of geological and mechanical factors on the critical disturbance pressure. Based on the established method, it predicts the risk of casing deformation in well X2. The following primary conclusions are drawn from this study. Multiple factors affect the critical disturbance pressure of fractures. The lower the critical disturbance pressure of fractures, the higher the risk of shear failure and casing deformation. The optimal orientation and strike of a dominant slip fault vary for different fault stress states. The higher the formation pore pressure, the lower the critical disturbance pressure of fractures; the greater the difference between the maximum and minimum principal stresses, the lower the critical disturbance pressure of fractures; and the smaller the friction coefficient of the fracture surface, the lower the critical disturbance pressure of fractures. The average critical disturbance pressure of the optimal dominant slip fault in well X2 is approximately 2.24 MPa, and multiple fracture activations are displayed throughout the well section, indicating a higher risk of casing deformation at the wellbore. When the critical disturbance pressure of the optimal dominant slip fault in well X2 is greater than 4.5 MPa, casing deformation will not occur. When the critical disturbance pressure of the optimal dominant slip fault in well X2 is low, and even if there is fracture activation, casing deformation might not occur at the wellbore. The case of fracture activation display but no casing deformation might be because no fractures are developed in the formation or that the orientation of the developed fractures is not within the activation angle range.